This invention pertains to microphysiometers, and more particularly to improved flow plungers for microphysiometers.
In a known microphysiometer, exemplified for example in Humphries et al. U.S. Pat. No. 5,104,804, rigid inner and outer sleeves covered at one end with a porous membrane, together with spacing means, are fitted together such that when the inner sleeve is fully inserted into the outer sleeve, the membranes are separated by a spacing means. The spacing means and the inner and outer membrane form a microchamber having living cells trapped within. The sleeves are adapted to hold the microchamber containing the cells adjacent to a silicon electrode that forms one wall of a flat microchamber. Cells are retained within the internal cavity of the porous microchamber while liquid is permitted to flow essentially, above, between and below the membranes and around the cells. The principal direction of flow of the liquid is parallel to the plane of the membranes and the surface of the silicon electrode. Changes in the media surrounding the cells, such as pH changes, can be measured by the silicon electrode.
The microphysiometer of Humphries et al. U.S. Pat. No. 5,104,804 has been commercialized in the CYTOSENSOR microphysiometer, that is made by Molecular Devices Corporation, Menlo Park, Calif. CYTOSENSOR is a registered trademark of Molecular Devices Corporation.
In the present plunger in the CYTOSENSOR device, the fluid flows tangentially across the upper surface of the cell-containing region, and the cells are in between the sensor and the flowing fluid. A consequence of this arrangement is that when fluid flow resumes during operation of the instrument, fresh medium must pass through the layer of cells before it gets to the surface of the sensor. If the cells are in a clot, then the surface of the sensor is accessible only by diffusion and not by bulk flow. The fluid exchange borders on the marginal for non-adherent cells and tangential flow is completely inadequate for thicker, contiguous samples such as tissue slices (typically 200-400 .mu.m rather than 50 .mu.m).
An object of the present invention sample is to provide an improved microphysiometer including a unique flow plunger and microchamber wherein the flow of medium is between the sample and a sensor and is then transverse and through the sample or around the sample, instead of tangential or across the sample.
Another object of the present invention is to provide an improved microphysiometer wherein fresh medium, from a passage means, flows directly between the cells and one wall of the microchamber, and where the wall is spaced from 10 microns to 200 microns from the sample for improving both the culture conditions (e.g., oxygenation) and the time response of the micro physiometer.
Yet another object of the present invention is to provide an improved microphysiometer wherein the time resolution of the acidification rate measurement is improved by increasing the rate of pH recovery when flow turns on. Further, time resolution for the physiological measurement is maintained by maintaining rapid diffusive communication between sample and sensor. Other objects and advantages will become more apparent hereinafter.